Domestication syndrome: White patches, baby faces and tameness

Jul 14, 2014

More than 140 years ago, Charles Darwin noticed something peculiar about domesticated mammals. Compared to their wild ancestors, domestic species are more tame, and they also tend to display a suite of other characteristic features, including floppier ears, patches of white fur, and more juvenile faces with smaller jaws. Since Darwin's observations, the explanation for this pattern has proved elusive, but now, in a Perspectives article published in the journal Genetics, a new hypothesis has been proposed that could explain why breeding for tameness causes changes in such diverse traits.

The underlying link between these features could be the group of embryonic stem cells called the neural crest, suggest the authors. Although this proposal has not yet been tested, it is the first unified hypothesis that connects several components of the "domestication syndrome." It not only applies to mammals like dogs, foxes, pigs, horses, sheep and rabbits, but it may even explain similar changes in domesticated birds and fish.

"Because Darwin made his observations just as the science of genetics was beginning, the domestication syndrome is one of the oldest problems in the field. So it was tremendously exciting when we realized that the neural crest hypothesis neatly ties together this hodge-podge of traits," says Adam Wilkins, from the Humboldt University of Berlin. Wilkins is an editor at Genetics and one of the paper's authors.

Neural crest cells are formed near the developing spinal cord of early vertebrate embryos. As the embryo matures, the cells migrate to different parts of the body and give rise to many tissue types. These tissues include pigment cells and parts of the skull, jaws, teeth, and ears—as well as the adrenal glands, which are the center of the "fight-or-flight" response. Neural crest cells also indirectly affect brain development.

In the hypothesis proposed by Wilkins and co-authors Richard Wrangham of Harvard University and Tecumseh Fitch of the University of Vienna, domesticated mammals may show impaired development or migration of neural crest cells compared to their wild ancestors.

"When humans bred these animals for tameness, they may have inadvertently selected those with mild neural crest deficits, resulting in smaller or slow-maturing adrenal glands," Wilkins says. "So, these animals were less fearful."

But the neural crest influences more than adrenal glands. Among other effects, neural crest deficits can cause depigmentation in some areas of skin (e.g. white patches), malformed ear cartilage, tooth anomalies, and jaw development changes, all of which are seen in the domestication syndrome. The authors also suggest that the reduced forebrain size of most domestic mammals could be an indirect effect of neural crest changes, because a chemical signal sent by these cells is critical for proper brain development.

"This interesting idea based in developmental biology brings us closer to solving a riddle that's been with us a long time. It provides a unifying hypothesis to test and brings valuable insight into the biology of domestication," says Mark Johnston, Editor-in-Chief of GENETICS.

Tests of the neural crest hypothesis may not be far off, as other scientists are rapidly mapping the genes that have been altered by domestication in the rat, fox, and dog. The hypothesis predicts that some of these genes will influence neural crest cell biology.

If so, we will have a much deeper understanding of the biology underlying a significant evolutionary event, Wilkins says. "Animal domestication was a crucial step in the development of human civilizations. Without these animals, it's hard to imagine that human societies would have thrived in the way they have."

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User comments : 9

Dr_toad

Many of these features can be seen in the most domesticated of humans. More evidence that we are not 'evolved'. Our domestication is ongoing as restless violence-prone young hotheads are being compelled to take up arms for some cause or other, and are then systematically culled.

This is one of the many benefits of Planned Conflict whether it be among street gangs, armed insurgents, or volunteer armies.

'The meek shall inherit the earth.' This is not a prediction but a Goal and a Promise.

Kill ratio must be artificially increased as modern warfare is too safe relative to traditional world wars with a kill ratio of 30% to satisfy objectives elucidated by Ghost. Thus is seen PSTD and Gulf War syndrome and lingering diseases of denatured uranium taking decades to take effect, and which acts to up the kill ratio to something proportionate to WWi stats

Kill ratio must be artificially increased as modern warfare is too safe relative to traditional world wars with a kill ratio of 30% to satisfy objectives elucidated by Ghost

Really? You're kidding right?

Sadaams army was getting to be a problem, according to him, so he sent it out into the desert where the US sir force carpet-bombed it into mush. In a few weeks perhaps 400k were killed.

This happened again in Afghanistan where the Taliban obediently led their forces north against the northern alliance. Same setup, nice straight entrenched formations suitable for carpet-bombing. Another army killed in a matter of days.

Soviets in Afghanistan lost perhaps 15k but killed perhaps 1.6M. This is victory by any measure. In Korea, the US lost 35k but perhaps 2M Asians died. This does not include the million or so who starved after the allies bombed the reservoir dams providing irrigation water in the closing months of the war.

Many of these features can be seen in the most domesticated of humans. More evidence that we are not 'evolved'. Our domestication is ongoing as restless violence-prone young hotheads are being compelled to take up arms for some cause or other, and are then systematically culled.

This is one of the many benefits of Planned Conflict whether it be among street gangs, armed insurgents, or volunteer armies.

'The meek shall inherit the earth.' This is not a prediction but a Goal and a Promise.

I immediately jumped to the same conclusion that we were doing the same thing to ourselves but a little thought and the fact that we are in and always have been in a constant state of conflict and war, we are selecting ourselves differently then our pets. It's not the meek that will inherit, it's the stupid. Our society selects for stupidity not intelligence.

not the meek that will inherit, it's the stupid. Our society selects for stupidity not intelligence

?? The smart figure out how to avoid war. The resourceful, ambitious, and pragmatic figure out how to emigrate while the stupid stay to fight for phony causes.

They at least know how to become officers and improve their chances of survival on the battlefield. 95% of enlisted germans died in stalingrad while 95% of senior officers survived.

There was an interview recently with a young palestinian US citizen who was among those told to evacuate gaza. He and his family had been visiting relatives. The interviewer asked him if he was sorry to be leaving. "Absolutely not!" was his reply. "I love the US." he said. Like, 'What, are you crazy? Who would be stupid enough to want to live here?'

-Lots of people, obviously. Smart people are in a distinct minority. The US was created for the express Purpose of skimming them from pops around the world and giving them the chance to comingle.

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